The presentation of moving images on a display has been a popular medium of communication for many years. As a result, many innovations have evolved to make movies and films capable of reproducing the visual and audible depth, robustness and acuity of the human senses. For example, digital image processing and communication techniques are capable of producing images and movies of exceptional high quality.
As with many industries, the evolution of technologies presents problems, particularly with respect to transitioning from an older technology to a newer technology. For example, in the wireless communications industry, much of the existing infrastructure and cellular telephones were designed to carry analog signals. Due to quality and capacity issues, digital systems and digital cellular telephones were designed. Since development of an entirely new digital system would take a number of years, however, an interim cellular telephone was developed that was capable of communicating using both analog and digital signals (sometimes referred to as “dual-mode” telephones).
The television industry is currently facing a similar problem. In particular, the television industry is presently transitioning from an existing video standard referred to as the National Television Systems Committee (NTSC) standard or the Electronic Industries Association (EIA) standard RS-170A developed in the late 1940s to the High Definition Television (HDTV) standard finalized in the early 1990s. A video signal “standard” specifically prescribes a video signal's synchronization timing, electrical voltage levels, and quality measures.
As a result, many television manufacturers are now developing televisions that are cable of displaying the present NTSC standard signals as well as the new HDTV standard signals. One key difference between these two standards, however, is the aspect ratio. The term “aspect ratio” refers to the dimensions of an image or picture which is calculated by dividing the image's horizontal width by its vertical height. In the present NTSC standard, the aspect ratio is a “4:3” aspect ratio, where 4 is the horizontal dimension and 3 is the vertical dimension. In other words, the horizontal dimension of the image is 1.33 times wider than the vertical dimension. By way of contrast, the HDTV standard calls for a “16:9” aspect ratio. When a 16:9 aspect picture is displayed on a 4:3 aspect ratio television, the horizontal width of the 16:9 aspect picture matches the horizontal width of the 4:3 aspect ratio television, but not the vertical height. Consequently, black bands appear at the top and bottom of the television screen. This is sometimes referred to as a “letterbox” effect, and is shown in FIG. 1.
FIG. 1 is a picture of a 16:9 aspect ratio picture displayed on a 4:3 aspect ratio television display. Displaying a 16:9 aspect picture on a 4:3 aspect ratio television creates a problem with respect to performing automatic digital convergence (also referred to as “auto-regi”, “auto-focus” and “flash-focus”) for the 16:9 aspect ratio picture. Automatic digital convergence (hereinafter referred to as “autoconvergence”) performs the function of displaying patterns to assist in the adjustment of the picture on the television display screen. These patterns are detected by, for example, sensors 108, 110, 112 and 114, which are placed at the top, bottom, left and right of the television display screen, respectively. Each sensor is essentially a solar cell that converts light energy into electrical energy. To perform autoconvergence the displayed picture must at least meet or overlap the sensors. When a 16:9 aspect ratio picture is displayed on a 4:3 aspect ratio display, however, the top and bottom edges of the 16:9 aspect ratio picture do not meet or overlap the top and bottom sensors (108, 110). Therefore, no patterns can be displayed on the top and bottom sensors.
FIG. 2 is a picture of a 4:3 aspect ratio picture displayed on a 16:9 aspect ratio television display. Similar to the problem described with reference to FIG. 1, a problem occurs when a 4:3 aspect picture is displayed on a 16:9 aspect ratio television. More particularly, the vertical height of the 4:3 aspect picture matches the vertical height of the 16:9 aspect ratio television, but not the horizontal width. Consequently, black bands appear at the left and right sides of the television screen. Therefore, when a 4:3 aspect ratio picture is displayed on a 16:9 aspect ratio television screen, the left and right sides of the 4:3 aspect ratio picture do not meet or overlap the left and right sensors (112, 114). Therefore, no patterns can be displayed on the left and right sensors.
In view of the foregoing, it can be appreciated that a substantial need exists for a method and apparatus capable of displaying a 16:9 aspect ratio signal on a 4:3 aspect ratio television, and vice-versa, while also performing autoconvergence on the displayed picture.